Voltage-gated calcium channels are important for neuronal functions such as neurotransmitter release and electrical excitability. Neurotransmitters can regulate these functions by effecting calcium channel gating. The long term goal of the proposed research is to understand the gating of neuronal calcium channels and how this gating is modulated by neurotransmitters to effect changes in neuronal activity. This proposal is focused on the N-type calcium channel in frog sympathetic neurons. N-channels are involved in neurotransmitter release and neurotransmitter inhibition of synaptic release has been correlated with the inhibition of N-type calcium current. The N-channel is the dominate calcium channel in sympathetic neurons and N-current has been well described at the macroscopic level. However, little is known about single N-channel gating. In addition, our evidence suggests that the N- channel was misidentified in previous studies from frog sympathetic neurons. The goals of the project are to examine the gating properties of the N-type calcium channel and determine the effect of neurotransmitters on N-channel gating. Toward these goals, we have identified a calcium channel which has the characteristics expected for the N-channel and differs from previously recorded 'N'-channels. Some of the questions which will be addressed are: (1) What are the criteria for the identification of single N-channels? (2) Do N-channels show modal gating like some other calcium channels? (3) What gating processes underlie N-channel inactivation? (4) How is N-channel gating altered by neurotransmitters to produce voltage-dependent inhibition? In addition, other calcium channels present in sympathetic neurons will be identified and characterized as they are encountered. This will allow us to better understand their role in the physiology of sympathetic neurons. This study is focused on the N-channel, but the process used in calcium channel identification will facilitate future work on neurons with a more complex mix of calcium channels. In addition, the knowledge gained about single N-channel gating will be important for the development of comprehensive models on calcium-dependent synaptic release and how that release can be inhibited by neurotransmitters.